Here are some resources for you:
King County bike resources, plus a link to a bike trail map:
Bicycling resources - King County Road Services Division
Seattle bike maps:
Seattle Department of Transportation: Bike Program
And back-up modes of public transport from Kent to Seattle, in case biking doesn't work out for you:
Sound Transit - Ride the Wave and
Metro Online Home Page
Where are you going to be staying in Seattle? Where do you have to go while you're there? The bus system in Seattle is surprisingly good, and downtown there is a large "fareless square."